1. Field of the Invention
The present invention relates to a borderless contact process, and more particularly, to a semiconductor device including a self-align stop layer for borderless contact process within shallow trench isolation. The provided semiconductor device can be simplified and result in fine borderless contact fabrication.
2. Description of the Prior Art
Recently, demand for semiconductor devices has rapidly increased owing to widespread use of integrated circuits (ICs). More particularly, as more than hundreds or thousands of electrical components are integrated into the ICs, a means for improving quality and reducing critical dimension of semiconductor devices has become imperative. Accordingly, with misalignment tolerance for the borderless contact formation, so silicon nitride layer must be used as a stop layer of borderless contact etching to avoid the oxide recess which will induce junction leakage currents.
In the sub-micro dimension, a borderless contact process is used to save the layout area. This usually needs a stop layer cap (for example, silicon nitride layer 300) in inter-layer dielectric (ILD) 320 layer to prevent junction from damage for shallow trench isolation (STI) 200 process during the contact etch step. In the contact etching step, first, oxide was etched and stooped on silicon nitride layer 300, and then the silicon nitride cap layer was etched and prevented from over-etching (e.g., oxide loss was controlled at the shallow trench isolation) to attack junction. This stop layer makes contact etching scheme complicated.
FIGS. 1A to 1D show cross-sectional views of a traditional semiconductor device, where the structure shown in FIG. 1D has additional gate oxide 120 and polysilicon layer 220. An N-type semiconductor device, for example, has a source/drain region 280B and 280C doped with N-type ions, which are usually designated as N.sup.+ regions. The substrate 100 usually has a P-type well, and the gate 220 is composed of polysilicon, and the spacers 260.
For submicron technology, the shallow trench isolation (STI) was employed for global planarization process. However, an oxide recess (especially as the corner of STI) will happen during the post-wet-dip treatment in STI process, and thus subthreshold kink effect will happen.
On the other hand, small contact was necessary to meet the requirement of the design rule, and thus the borderless contact was used to increase the critical dimension of contact size and process margin for small contact formation.